Pro-adhesive sol-gel coatings for fibers in epoxy resin composite materials
Anna Szczurek, Michał Barcikowski, Justyna Krzak
Quarterly No. 4, 2017 pages 211-215
DOI:
keywords: sol-gel, organosilica coatings, glass fibers, carbon fibers, aramid fibers
abstract Inadequate adhesive strength of the reinforcing fibers to the matrix in composite materials causes their delamination, which reduces the bearing capacity and durability of the defected product, and in the case of pressure vessels or pipelines, may cause their depressurization. One of possible methods to improve the adhesive strength is to coat the reinforcing fibers by the sol-gel method with organosilica coatings. Silane coatings serve two purposes: 1) the film binds chemically to the surface of the glass fiber, 2) wetting is improved by an increased chemical affinity of the resin to the fiber. Carbon and aramid fibers are usually not coated in this manner, resulting in inferior adhesive properties. In this study, organosilica materials were obtained by the sol-gel method using various silica precursors: methyltrimethoxysilane (MtMOS), ethyltriethoxysilane (EtEOS) and tetramethoxysilane (TMOS). The materials were deposited on glass fiber and hybrid carbon/aramid fiber textiles, resulting in a change in the surface properties. The chemical structures were characterized by Raman spectroscopy, indicating the presence of groups characteristic for silica, as well as the presence of functional organic groups connected by silicon-carbon bonds. The surfaces of the coated fibers were observed by scanning electron microscopy (SEM), indicating undesirable fiber bonding by the coatings obtained using the MtMOS and TMOS precursors, while no such bonding was observed for the coating obtained using the EtEOS precursor. The wettability of the glass fibers by epoxy resin was measured using the electro-optical method, revealing that the coatings made of the MtMOS and TMOS mixture improved the wettability of the fibers with epoxy resin, facilitating adhesion.